Falling can be a serious problem, especially for the elderly and those with musculoskeletal problems. During gait, falling may result from "slips", a condition that occurs during stance phase when friction is inadequate to meet slip-resistance needs, or "trips," when there is inadequate ground clearance during swing phase. To determine possible mechanisms for falls in patients with decreased strength and normal joints, we have begun studies in patients with muscle disease. Measurements of required slip-resistance and ground clearance were made in a patient with Inclusion Body Myositis (IBM) and a high incidence of falls, using two strain gauge force plates and a passive infra-red motion analysis system. Manual muscle testing was performed to measure relative muscle strength, and a questionnaire was used to gather facts pertinent to falls. Marked differences were seen between the right and left legs. Ground clearances for the right toe and heel did not seem to put this patients at risk for tripping. Required slip-resistance at heel-strike was abnormally high at 0.66 +/- 0.03 (n=6), consistently above normal values (less than 0.25) and architectural guidelines (0.50). This put the patient at risk for slipping on the right foot. Although questionnaire responses did not identify slipping as a precursor to falls, knowledge of the increased risk was considered useful for patient safety. For the left leg, abduction was pronounced during swing, which terminated with a prolonged medial sweep of the foot over the final 40% of swing. Ground clearance of the left heel was below 1 cm during this sweep, increasing the likelihood of tripping. In this situation, the patient could fall because weak hip and knee musculature may not be strong enough to stabilize the body. Indeed, the patient did identify tripping on the left side as a precursor to falls. We conclude that detailed biomechanical analyses identify gait characteristics that put patients at risk for falling, and may facilitate directed clinical interventions to prevent falls. We are expanding the scope of this study to other IBM patients.